5 files changed, 44 insertions, 12 deletions

diff --git a/arch/um/include/asm/processor-generic.h b/arch/um/include/asm/processor-generic.h
index c03cd5a02364..90469031297b 100644
--- a/arch/um/include/asm/processor-generic.h
+++ b/arch/um/include/asm/processor-generic.h
@@ -21,6 +21,7 @@ struct mm_struct;
 struct thread_struct {
         struct task_struct *saved_task;
         struct pt_regs regs;
+        struct pt_regs *segv_regs;
         int singlestep_syscall;
         void *fault_addr;
         jmp_buf *fault_catcher;
diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
index 021104d98cb3..75298d3358e7 100644
--- a/arch/um/include/shared/os.h
+++ b/arch/um/include/shared/os.h
@@ -227,6 +227,7 @@ extern void block_signals(void);
 extern void unblock_signals(void);
 extern int get_signals(void);
 extern int set_signals(int enable);
+extern int os_is_signal_stack(void);
 
 /* util.c */
 extern void stack_protections(unsigned long address);
diff --git a/arch/um/kernel/sysrq.c b/arch/um/kernel/sysrq.c
index 33cc72e26c6e..7122bf9c753e 100644
--- a/arch/um/kernel/sysrq.c
+++ b/arch/um/kernel/sysrq.c
@@ -12,6 +12,7 @@
 #include <linux/module.h>
 #include <linux/sched.h>
 #include <asm/sysrq.h>
+#include <os.h>
 
 struct stack_frame {
         struct stack_frame *next_frame;
@@ -48,29 +49,42 @@ static void print_stack_trace(unsigned long *sp, unsigned long bp)
 /*Stolen from arch/i386/kernel/traps.c */
 static const int kstack_depth_to_print = 24;
 
-static unsigned long get_frame_pointer(struct task_struct *task)
+static unsigned long get_frame_pointer(struct task_struct *task,
+                                       struct pt_regs *segv_regs)
 {
         if (!task || task == current)
-                return current_bp();
+                return segv_regs ? PT_REGS_BP(segv_regs) : current_bp();
         else
                 return KSTK_EBP(task);
 }
 
+static unsigned long *get_stack_pointer(struct task_struct *task,
+                                        struct pt_regs *segv_regs)
+{
+        if (!task || task == current)
+                return segv_regs ? (unsigned long *)PT_REGS_SP(segv_regs) : current_sp();
+        else
+                return (unsigned long *)KSTK_ESP(task);
+}
+
 void show_stack(struct task_struct *task, unsigned long *stack)
 {
         unsigned long *sp = stack, bp = 0;
+        struct pt_regs *segv_regs = current->thread.segv_regs;
         int i;
 
+        if (!segv_regs && os_is_signal_stack()) {
+                printk(KERN_ERR "Received SIGSEGV in SIGSEGV handler,"
+                                " aborting stack trace!\n");
+                return;
+        }
+
 #ifdef CONFIG_FRAME_POINTER
-        bp = get_frame_pointer(task);
+        bp = get_frame_pointer(task, segv_regs);
 #endif
 
-        if (!stack) {
-                if (!task || task == current)
-                        sp = current_sp();
-                else
-                        sp = (unsigned long *)KSTK_ESP(task);
-        }
+        if (!stack)
+                sp = get_stack_pointer(task, segv_regs);
 
         printk(KERN_INFO "Stack:\n");
         stack = sp;
diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index 5c3aef74237f..974b87474a99 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -206,9 +206,12 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
         int is_write = FAULT_WRITE(fi);
         unsigned long address = FAULT_ADDRESS(fi);
 
+        if (regs)
+                current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
+
         if (!is_user && (address >= start_vm) && (address < end_vm)) {
                 flush_tlb_kernel_vm();
-                return 0;
+                goto out;
         }
         else if (current->mm == NULL) {
                 show_regs(container_of(regs, struct pt_regs, regs));
@@ -230,7 +233,7 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
 
         catcher = current->thread.fault_catcher;
         if (!err)
-                return 0;
+                goto out;
         else if (catcher != NULL) {
                 current->thread.fault_addr = (void *) address;
                 UML_LONGJMP(catcher, 1);
@@ -238,7 +241,7 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
         else if (current->thread.fault_addr != NULL)
                 panic("fault_addr set but no fault catcher");
         else if (!is_user && arch_fixup(ip, regs))
-                return 0;
+                goto out;
 
         if (!is_user) {
                 show_regs(container_of(regs, struct pt_regs, regs));
@@ -262,6 +265,11 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
                 current->thread.arch.faultinfo = fi;
                 force_sig_info(SIGSEGV, &si, current);
         }
+
+out:
+        if (regs)
+                current->thread.segv_regs = NULL;
+
         return 0;
 }
 
diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 905924b773d3..7b605e4dfffa 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -304,3 +304,11 @@ int set_signals(int enable)
 
         return ret;
 }
+
+int os_is_signal_stack(void)
+{
+        stack_t ss;
+        sigaltstack(NULL, &ss);
+
+        return ss.ss_flags & SS_ONSTACK;
+}